Access to the inner ear, specifically the cochlea, is required for cochlear implant (Cl) surgery in which an electrode array is used to stimulate the inner ear allowing deaf people to hear. More than 80,000 CIs have been placed worldwide with the vast majority performed in the United States. Projections indicate that up to 750,000 Americans with severe-to-profound hearing loss may benefit from Cl. Furthermore, advances in pharmacology hold out the prospect that drug delivery to the cochlea may treat. Current techniques of cochlear access are based on wide surgical excavation via drilling of the mastoid region of the temporal bone (the bone which houses the inner ear). This surgery, which takes upwards of 2 hours, uses visual feedback to avoid damage to vital structures also encased in the temporal bone most notably the facial nerve injury of which can cause drooping of the face. The hypothesis of this proposal is that less invasive cochlear access can be achieved by using image guided surgical (IGS) techniques. Using IGS we have demonstrated the concept of percutaneous cochlear access as a single pass of a surgical drill from the lateral skull to the cochlea without injury to adjacent vital structures. Potential benefits of this minimally-invasive technique over the traditional, wide-surgical exposure include (1) time and cost savings, (2) standardization of surgical technique allowing more surgeons the ability to perform this procedure, and (3) same-day service (surgical implantation and activation on the same day). We envision such a minimally-invasive technique to become the LASIK procedure of the ear efficiently restoring hearing via Cl and/or drug delivery. To test our hypothesis, herein we propose a multi-center study looking at the use of patient-specific drill guides built via rapid-prototyping based on pre-operative CT scans. The drill guide will direct a surgical drill from the lateral skull to the cochlea without injury of adjacent vital structures. This device is FDA-approved and currently used in neurosurgical applications (deep brain stimulator placement in patients with intractable seizures). During years 1 and 2, we propose a validation study whereby the drill guide will be attached to patients after traditional, wide-exposure Cl surgery to ensure accurate trajectory. During years 3 and 4, we propose to clinically use the drill guide to obtain cochlear access during Cl surgery. Concurrent with the validation phase (years 1 and 2), we propose continued refinement of technique including development of (i) safety shut-off should the facial nerve be threatened by the drill, (ii) automated surgical planning software, and (iii) drill press to be mounted on the drill guide for clinical use of the drill guide during years 3 and 4. [unreadable] [unreadable] [unreadable]